Universal weld current analyzer



May 8, 1962 M. A. FERGUSON A3,034,057

UNIVERSAL wELD CURRENT ANALYZER :5 sheets-sheet 1 Filed Jan. 16, 1959 INVENTOR.

H 7 TOR/VE Y May 8, 1962 M. A. FERGUSON UNIVERSAL WELD CURRENT ANALYZER 3 Sheets-Sheet 2 Filed Jan. 16, 1959 A TTORNEY May 8, 1962 M. A. FERGUSON 3,034,057

UNIVERSAL WELD CURRENT' ANALYZER Filed Jan. 16, 1959 3 Sheets-Sheet 3 0 /00 HEAT 0 6a H54 r l l wao/N@ I co/voucra/P l ,7H /N 1 mf? f/f if Tanon/,4L l

I Il i| V \l GENE/M705 MEMORY INVENTOR.

ATTORNEY are 3,034,057 UNF/'ERSAL WELD SERPENT ANALYZER Millard A. Ferguson, Utica, Mich., assigner to General Motors Corporation, Detroit, Mich., a corporation oir' Delaware s Filed dan. lo, i359, Ser. No. 737,277 l-'tllaima (Cl. 32a-H2) This invention relates to measuring and indicating means and more particularly to means tor accurately measuring and indicating secondary welding current in a production welder regardless of whether or. not the current has been phase shifted to provide heat control.

Many diiierent high current measuring means have in the past been designed andV some have been useful in `measuring and indicating the secondary welding current which flows to produce welds when such current is a pure sine wave and not phase shifted for heat control. However, no indicating systems are known which will give accurate reading of secondary current in a Welder when phase shifting is applied to vary the amount of heat applied for welding.

It is essential in producing duplicate welds that are uniform in quality that the same welding conditions exist, namely, current, time, and pressure for the weld. in order that duplicate welds are made, welding machines should be periodically checked to assure that none ot these factors are varied. Also, in initialiy installing a i ew machine or adjusting a machine to accommodate a new part, it is necessary to carefully adjust the current so that burning will not occur and yet a iirm weld be obtained. Many other instances occur in which it is necessary to accurately check 'or measure the secondary weldin g current.

It is therefore an object in making this invention to provide a device for accurately measuring secondary welding current in a welding machine under either phase shifted r vnon-phase shifted conditions.

It is a further object in making this invention to provide a secondary current meter which can be `simply attached to a welding machine without disturbing the normal Welding operation. Y

it is a further object in making this invention to provide a current meter for a welding machine which will measure phase shifted current in terms or" RMS. values which is portable, will operate from available power supply, and retains a reading long enough to be easily noted.y

With these and other objects in View which will become apparent as the speciication proceeds, my invention will be best understood by reference to the following specificaportions of my novel 'weld current meter..

FIGURES 2 and 2A are parts forming a complete cir- Fnite @attent @il cuit diagram of a welding current meter embodying my n invention; and

FIGURE 3 is a set of curves illustrating the wave forms appearing at dilerent portions of the system together with an associated block diagram indicating the location of the waves so that the form. at any point can be quickly and readilyascertaincd. v

The principal lfeatures of tms current measuring system consist generally in obtaining a signal voltage or wave which is proportional to the rate of change of the welding current, putting said signal voltage through three stages of electronic `circuits to obtain an RMS. value of the welding current'and then indicating its value.

' More speciiically referring to FIGURE l, a torroidal coil ii is placed around a part of the secondary welding circuit and has a voltage induced therein by the flow of welding current which is proportional to the dilerental ansias? a a of said secondary current. This voltage is applied to an attenuator 4 and thence to a rst integrator 6. This stage o changes the torroidal output voltage back to a voltage that is proportional at all times to the welding current and by integrating a voltage that has been differentiated, voltage of similar wave form to that of the original current is obtained. This signal is next applied toa squared 'function output circuit 8 which generates a D.C. Output voltage proportional to the square of the input voltage. This signal is next amplified in ampliiier ltl'which converts the low amplitude DC. pulses into high-level A.C. signals. These are then applied to a second integrator i2 where the signals are again integrated to provide an output that is now proportional to the current squared.

r This signal is a voltage withY a peak to peak value whose square root is proportional to the R.M.S. value of the welding current, and this is lastly applied to the memory and indicating meter i4.

lt is relatively simple to obtain a signal voltage from a welding circuit which is proportional to the R.M.S. value of the welding current if the current owing is substantially a sine wave and has not been phase shifted t0 control the heat. However, where the weld heat has been adjusted to less than by shifting the phase so that use is made of only a fraction of each half cycle the wave )form becomes irregular, the peak value is not strictly proportional to the R.M.S. value and it is more diihcult to obtain signals proportional to the R.M.S. value of the current. rl`he general formula for RIVLS. current in the present measuring circuit the squared function generator is used to give a signal proportional to the square ofthe current, the second integrator provides the integration from O to time period T 4and the rest of the formula is taken `care of in the meter circuit. By the use of this system an indicating signal proportional to the Rit/LS. current can be obtained 4for any current wave shape.

Having now described the weld current analyzer in general, reference is made to FGURE 3 which specifically identities the wave forms obtained at the various circuit locations. At the lefthand side of FIGURE 3, are block diagrams labelled to identify the certain parts of the sys,- tem in horizontal alignment with each of two columns of wave forms which are found at these locations, one representing a sine wave of non phase'shifted current labelled 100% heat and the second columnspacedto the right showing a phase shifted current which might be any percentage but for illustrative purposes is shown at 60% heat. At the top of FiGURE 3 at theleft, there is showndia-` grammatically a welding conductor 18. Curve 20 just t0 the right thereof, shows the sine wave of current iiowing in the secondary circuit. of the Welder for non-phase shifted 100% heat. Farther to'the right on the same horizontalline in the graph there is vshown a plurality of disconnected pips 2,2 which are obtained when phase shift isemployed to decrease the total heatapplied. These are representative of the welding current tlowing in the secondary circuit vunder these circumstances. When the torroidal coil 2 is placed around a portion of the secondary circuit with the indicated current flowing therein; there is induced in said coil a Voltage shown graphically as 2d which is proportional to the rate of change of the current 20 ,when there is no phase shift. When a'phase shift is utilized, voltages such as those diagrammatically shown at 26 are induced in the torroidal coil by the pips Z2. The voltage from the torroidal coil is then applied to the tirs/t integrator 6 andrtlns stage changes the output voltage back to a voltage which is pro? portional at all times to the welding current and when no phase shift is applied, is shown at 28. This curve therefore resembles the current curve as originally shown at 20 but does not have the same amplitude, being less. Similarly, when phase shift is used, smaller pips 30 which again resemble pips 22 at the top of the column are obtained.

The output of the first integrator is fed into the squared function generator 8 and this circuit takes the voltage from the integrator and modifies the Vsame by squaring it as shown in curve -`82 for 100% heat land in like manner the partial heat phase shifted pips at 34. These waves `are then fed into the amplifier and produce high amplitude A.C. output voltages 36 and 38 respectively as shown by the curves opposite said amplifier. These vol-tages are next appliedto a second integrator 12 which produces waives 40 and 42 whose peak value is proportional to the current squared. This output is at this point a voltage having a peak to peak value as shown lat M whose square weld current analyzer as shown in FIGS 2 and 2A, there is shown therein Ythe same torroidal pickup coil 2 which is connected to the attenuator section enclosed by dash and dotted outlines at 4. This section includes a voltage divider including a plurality of resistances 44, 46, 48, 50 and 51 which are connected in series across lines 52 and 54 which extend from the terminals of the torroidal coil 2. Resistance 44 yalso has an adjustable tap 56 which can be moved over the same to shunt out a portion of the resistance and therefore change its effect in the circuit. This voltage divider is connected to a multi-position switch including a movable arm- 58 and 'a plurality of stationary contacts 60, 62, 64, 66 and 68 which the arm 58 may engage in different positions. Contact 60 is connected to an intermediate point between resistances 44 and 46; contact 62 to an intermediate point between resistances 46 and 48; contact 64 to an intermediate 'point between resistances 48 and 50; land contact 66 to la similar intermediate point between resistances 50 and 51. Stationary contact 68 of this multi-position switch is connected through line 70 toa part ofthe voltage supply which will be described later and is for calibration purposes. Movement of the movable `arm 58 around to engage the various stationary contacts changes the proportionateamount of the signal picked up by the torroidal coil and fed 4to the rst integrator stage.

The rst integrator is shown in dash and dotted outlines at 6and includes an electron tube 72 having a plate 74, control grid 76, and cathode 78. The movable arm 58 of the selector switch vis directly connected through a resistance 80 to the control grid 76 of the tube 72. A bypass condenser 82 is connected between said grid and ground to integrate the signals. The plate is supplied with the proper voltages through limiting Vresistor 84 and thence -to a power supply indicated by A which will be connected to another portion of the power circuit similarly indicated. This is to simplify the circuit diagram. The cathode 78 of the Vtube 72 is connected through resistance 86 with movable switch arm 88 which is mechanically ganged with the first rotary switch arm 58. This second arm l88 is adapted to move over a series of stationary contacts 90, all of which are conductively connected together and'to the line 54 from the torroidal coil. Thus, as soon ias the arms S8 and 88 are moved from their original deenergized position, arm -88 will connect line 54 to the cathode string of the tube 72, for any other position of the switch. Switch arm 88 may also engage stationary contact 91 which is a calibrating contact similar to contact 68 for switch arm 58. Contact 91 is connected through line 93 with a further portion of the voltage supply system to be described. The switch arm 88`is likewise connected to one terminal of the primary coils 92 and 94, which are the primary coils of a transformer T-1 and are connected in series with the center tap grounded. The opposite terminal is connected through line 96 to la third rotary ganged switch arm 98 which mo'ves simultaneously with arms 58 and 88 as shown by the dash line connecting the three. position such as that shown and is provided inV order Ito feed in calibrating signals through the circuit 102 connected thereto. During normal metering, this circuit is disconnected.

Thus, the effective signals generated in the torroidal coil by the fiow of secondary current in the Welder are adjusted in strength by movement of the switch arms 88 and 58 attenuated and supplied to the input of the tube 72 where they are integrated. This tube and its associated circuit including resistance 80v and condenser 82 in the input and resistance 86 and transformer T-l in the output is known as a bootstrap integrator. Such integrators are known and their operation described in a book entitled Wave Forms, Vol. 19 of the Radiation Laboratories Y Series published by McGraw-Hill in 1949. The output of the integrator 6 is applied to the squared function generator 8 through the transformer T-l. This squared function generator 8 consists of a plurality of pairs of precision resistors connected in series lacross the power line 104 and ground line 106. The value of these sets of resistors Varies from left to right, those of higher value being shown at the left. The purpose of this section is to produce a squar-ing effect for the current. At the intermediate point for each pair of resistances, such as CDEFG, a voltage is developed by the application of power across the pair from line 104 to ground. These voltages increase from ileft to right starting, for example, as a fraction of a volt and increasing to something in excess of six volts at the righthand end. Thus, resistances 108 and 110 connected across the power line 104 and ground line 106 would develop, for example, one volt at point C. A plurality of rectifiers 103, 105', 107 and 109 are connected between points C and D, D and E, E and F, and F and G. A fur- :ther rectifier 111 is connected to point C and to the upper terminal of resistor 113, the opposite terminal of which is connected to ground line 106;

The output of the first integrator section is applied to primary 92 of transformer T-1 in the cathode line of tube 72. This transformer has a pair of primary windings 92 and 94 previously described, and a pair of secondary lwindings 118 and 126. Winding 118 has one terminal connected through line 120 and rectifier 115 to one end of resistor 113. The other terminal of secondary winding 118 is connected directly through line 124 to one control electrode 136 of the duo-triode tube 132 in amplifier section 10. A biasing resistor 121 is connected between line 124 and ground across which the control voltage representative of one-half cycle is developed. In n like manner, one terminal of the second secondary 126 is connected through line 123 and rectifier 125 to the same end kof resistor 113. The remaining terminal of winding 126 is connected through line 122 tothe other control grid 134 of the second one-half of the duo-triode amplifying tube 132. VBiasing resistor 127 is connected between line 122 and ground and across this resistance a control voltage is developed proportional to the amplitude of the alternate half cycle.

As the integrated voltage across primary 92 increases, a voltage is developed across secondary 118 that is so poled as to match or exceed the voltages at C, D, E, etc. and therefore create an increasing number of parallel paths through resistances 110, 131, 133, etc., the greater the amplitude.l With more resistances in parallel the lower will be the effective resistance in circuit and the great-V er the ow of current so as the voltage at secondary 118 increases, an effective squaring of the current is obtained. This squared current flows through resistance 121 to Arm 98 engages stationary contact 100 at one .man

ground also, and this develops an effective squared voltage on line 124 to apply to control grid 136. The circuit in which this control voltage is developed for the iirst half cyclemay be traced as follows: ground, line d, through several resistances 113, Htl, 131 or 133 depending on the signal voltage, rectifier 115, line 12h, secondary winding 11S, line 124i, resistance 121 to ground. Thus, the signal voltage applied to winding 118 develops an effective squared voltage across resistance 121 which is applied to grid 136. For the next half cycle, an effective squared voltage is developed in the alternate circuit including secondary' winding 12o to obtain a biasing voltage across the resistance 127 to be applied to control grid 134 of tube 132. The positive squared function pulses are shown by the waves 32 on the graph of FIG. 3. Thus, each half wave in the output of the lirst integrator produces a positive pulse for alternate application to the control grids 134 and 136 of tube 132.

ISection 1li including tube 132, is an amplifying section, thef output of which is applied to the second integrator 12. The input is applied to grids 134 and 136 and the two plates of the tube 14d and 14o are connected to opposite terminals of a primary winding 14h of the transformer '113, the center tap if which is supplied with power from the main voltage supply indicated as W and later to be described. Condenser 15d is connected across the primary winding 14S. The cathodes 138 and Mtl are self biased through resistance 142 connected to ground. This section not only amplies the squared wave form but also changes it back to alternating current as shown at 36 and 3S of FIGURE 3.

Secondary winding 152 ofthe transformer T-Si to which this signal wave is applied is connected through lines 154 and 162i to the second integrator section 12. rthis second integrating section which is of the same basic construction as the lirst integrator section includes an electron tube 156 having a plate 158, a control grid 416d and a cathode 162. The cathode is connected through a biasying resistor 16d and an output transformer winding 166 in series therewith to ground.y rlhe line 154i from the transformer winding 152. in the amplifier 1u is connected Ato an intermediate point between the resistance 16d and the winding 166. The other side of the transformer Winding 152 of the amplifier is connected through conductor 16S to one terminal of a resistor 17d which is connected through a series condenser 172 to ground and also directly to the control grid loll of tube e. A condenser 174 is connected between the plate 153 and ground, said 'plate being likewise connected through limiting resistor 178 to the power supply of proper voltage indicated as B Thi:- output of the second integrator section 12 is in the wave form shown at du or 4t2 in FIG. 3 and is applied through transformer T-f to the metering and memory section 1d. The primary 165 of the transformer T--t is in the cathode circuit of tube 156 and supplies the secondary coil 194i with the output signal. The secondary 194 is connected directly across a high pass ilter 1% which is designed to pass frequencies above 60 cycles per second. The output of the lter 1% is applied through resistance 198 to a voltage doubler section which includes condensers Ztl@ and 2&2 and rectiers 192 and 26d. Ground reference for the voltage doubler section is obtained from a point between condenser 2102 and rectifier 204 through line 2do. From this voltage doubler section the signal is applied to control grid 136 of duo-triode tube 18d by line 190. Plates 1S@ and 1%2 of tube 1de are connected to the power supply indicated by B+. Grid 188 of the second triode section is directly grounded.

Cathode 21d is connected through resistance 216 to one terminal of resistance 218. Similarly, cathode 220 of tube 1h45 is connected through resistance Z22 to the remaining terminal of resistance 218. An adjustable tap 224 movable over resistance'ZilS is grounded. Connected in series circuit across the cathodes 214i and 22d are a meter M, a resistance 226, and a variable resistance 228.

A reset switch is provided which has two armatures 23S and 23u, spring biased to the left as shown in FIG. 2A. Armature 2.325 is adapted to bridge stationary contacts 23o and 23d when in its lefthand position and completes a circuit for one portion of the power supply to be described. This switch is normally closed. The second armature is insulated from the first but mechanically ganged Ato move with the same and when forced to the right by pressure, bridges the two stationary contacts 20S and 21u. Contact 208 is connected to ground and contact 21@ through resistor 212 to grid 1&6. When this switch is closed, the charge is taken o the grid and the meter returns to Zero.

ln initially setting the device without any input signal, the adjustable tap 2.24- is moved until there is an equal amount of current flow through each half of the tube 134i. Under these conditions there will be no unbalance at the cathodes and the meter M will read zero. As the signal is applied from the output of the voltage doubler more current llows through the lefthand side to unbalance the two and current flows across the meter circuit. The peak voltage obtained from any given input signal remains on the grid ld for some considerable time so that the operator can easily read it.V

The power supply for this system is obtained from a receptacle 254 which can be plugged into any convenient volt system and which supplies power to lines 255 and 252B. A master switch 26d having two insulated blades independently connects line 256 to line lo?. and line 25d to line 26d to supply power to a power transformer. This power transformer includes a number of different windings, tl e primary winding being separated into two parts, Zoo and 263, both of which are connected across the linesV 262, and Zed and which induce voltages in a number of secondary windings 27d, 272, 274 and 2.76. A neon pilot light 275 is connected across lines 264i and 262 to stabilize the supply. The winding 272 supplies power for the variousvacuum tube lilaments and is merely marked with terminals XX to indicate this. Secondary 27d supplies power to power lines 93; and '7d for calibrating the attenuator section. Secondary Z/dis center tap grounded and connected through a rectiiier network 27.3 and also through a i'ilter including a choke 2Std and a condenser 28?. to supply DC. power to a point W which is connected to the paired point W in the amplitier section. A voltage regulating section includ-ing regulator tube 22d-t provides regulated DC. power to a point VA which in turn feeds said power to point A in the rst integrator section.

In the operation of this system the torroidal coil Z is placed around one of the welding electrodes through which welding current flows when the Welder is operated. The gang switch S-tlS-Qi is placed in one of its intermediate positions depending on the amplitude of the signal developed. The Welder is then operated with the resultant induced current in the coil and development of signal wave forms at the locations as indicated on FlG. 3. The meter M reads a peak value which is proportional to the Rit/LS. value of the current regardless of whether it is a full sine wave or is phase shifted for heat control and is retained for a period of time. After reading, the operator may depress the plunger 239 to take off the reading and prepare for the next measurement.

Moving gang switch 58-S393 to its uppermost position will apply the voltage from secondary 27d of the power transformer directly to the first integrator stage. Movement of this switch to its lowerrnost position opens all circuits to the attenuator and first integrator and connects some outside signal source plugged into terminals lill and to the transformer T-1 to calibrate other parts of the equipment.

I claim:

l. ln means for measuring current flowing in conductors in which the wave form may be irregular and non-uniform in shape, a pickup coil adaptedto be supported in juxtaposition to a conductor carrying current it is desired'to measure, said pickup coil having voltages induced therein which are proportional to the differential of the current in the conductor,V first integrating means connected to the pickup coil to integrate the signal and obtain a voltage proportional to the current, squared function generating means connected to the first integrating means to provide an effective squared signal, second integrating means connected to the squared function generating means to further integrate the signal and ob-l tain a voltage whose peak is proportional to the R.M,.S. current in the conductor and memory indicating means connected to the second integrating means to indicate the R.M.S. value of the current and hold the position for sufficient time to be easily readable.

2. In current measuring means adapted to be utilized with a welding machine having phase shift heat control to measure welding current in a conductor thereof, a pickup coil adapted to be supported in juxtaposition to the conductor carrying current it is desired to measure, said pickup coil having voltages induced therein which are proportional to the differential of the current in the conductor, first integrating means connected to the pickup coil to integrate the signal and obtain a voltage proportional to the current, squared function generating means connected to the first integrating means to provide an effective squared signal, second integrating means connected to the squared function generating means to further integrate the signal and obtain a voltage whose peak is proportional to the R.M,.S. current in the conductor, memory indicating means connected to the sec-A ond integrating means to indicate the RJVLS. value of the welding current and hold it for sufficient time to be easily readable, and grounded switching means connected to the memory indicating meansto remove the reading on the same when he switching means is closed to put the same in condition for the next reading.

3. yIn current measuring means adapted to be utilized with a welding machine having a phase shift heat control to measure welding current in a conductor thereof, a pickup coil adapted to be supported in juxtaposition to the 'conductor carrying current it is desired to measure, said pickup coil having voltages induced therein which are proportioned to the differential of the current in the conductor, first integrating means connected to the pickup coil to integrate the signal and obtain a voltage proportional to the current, squared function generating means connected to the first integratingmeans to provide an effective squared signal, second integrating means connected to the squared function generating means to further integrate the signal and obtain a voltage whose peak is proportional to the R.M..S. current in the conductor, filtering means connected to the output of the second integrating means to remove unwanted low frequency, transients voltage doubling means connected to the output of the filtering means, and a balanced bridge indicating circuit including a meter connected to the voltage doubling means to give an indication of the signal applied which is proportional to the RMS. welding current.

4. In current measuring means adapted to be utilized with a welding machine having phase shift heat control to measure welding current in a conductor thereof, a pickup coil adapted to be supported in juxtaposition to 3a conductor carrying current it is desired to measure, said pickup coil having voltages induced therein which are proportional to the differential of the current in the conductor, first integrating means connected to the pickup coil to integrate the signal and obtain a voltage proportional to the current, squared function generating means connected to the first integrating means to provide an effective squared signal, second integrating means connected to the squared function generating means to further integrate the signal and obtain a voltage whose peak is proportional to the R.M.S. current in the conductor, filtering means connected to the output of the second integrating means to remove unwanted low frequency transients, voltage doubling means connected to the output l of the filtering means, a balanced bridge indicating circuit including a meter connected to the voltage doubling means to give an indication of the signal applied which is proportional to the R.M.S. welding current, and manual grounded switching means connected to the balanced bridge indicating circuit to remove'the signal applied and prepare the meter for the next measurement.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Publication: Toroid Measures Spot Weld Current, by P. M. Zimmerman, pages 132 and 133 of Electronics, Dec. 1, 1957. 

